I completed a mission and did everything on it and it still wont go away from the pipboy. What do I do?

What mission?

the heartache by the number mission

So you're already got Cass as follower and finished her side quest ?

I don't have her as a follower, but I completed her side quest and she will let me become her follower. I'm using boone. Is cass better than boone?

Heartache by the Number doesn't end until you finish Cass's personal quest, meaning you have to take her as a companion for a period of time and 'do stuff' etc. If you did all that, then...dunno.

As to which is better...that's really subjective. In the old days, Boone was much better because he was glitchy-overpowered, but these days...it's probably about equal & just depends on your personal playstyle & likes. They both have the exact same Tag skills. If you do Cass' personal quest she can get extra hitpoints and extra gun damage, but w/her Perk she's more geared towards shotguns, where Boone is sniper. So do you want a silent, grumpy sniper, or a very very talkative, alcoholic shotgunner.

thanks!